Transmission actuator

Abstract

A transmission actuator has a torque generating mechanism for generating a torque from a drive shaft, a speed reduction mechanism for multiplying a torque from the torque generating mechanism through a differential motion produced by a difference in gear ratio between a gearset of a first internally toothed gear and a first externally toothed gear and a gearset of a second internally toothed gear and a second externally toothed gear, a motion direction changing mechanism for converting the torque multiplied into a thrust and a friction engagement mechanism for transmitting power from an input shaft to an output shaft by virtue of the thrust so converted, wherein the drive shaft is made hollow so that the input shaft and the output shaft are disposed in a hollow portion of the drive shaft.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to a transmission actuator for use in a four-wheel drive mechanism or a limited slip differential mechanism for automobiles, or in general industrial machinery.[0003]2. Description of the Related Art[0004]A document referred to as Patent Literature No. 1 below is known to describe as a conventional transmission actuator an electric actuator in which a motor is provided externally. An actuator for friction engagement devices described in JP-B-08-019971 will be described in detail below.[0005]FIG. 7A is a half sectional view of an actuator 50 for friction engagement devices.[0006]As shown in FIG. 7A, a friction multi-plate clutch 65 of the actuator 50 for friction engagement devices is provided between a clutch hub 66 connected to a front wheel side hollow shaft 62 and a clutch drum 67 connected to a rear wheel side hollow shaft 61, and the torque (rotational torque) of a motor 71, which is a...

AI Technical Summary

Benefits of technology

[0020]According to the arrangement as set forth in the fifth aspect of the invention, speed reductions through a number of combinations of reduction gear ratios can be made possible by providing the ring gear on the inner circumferential surface of the transmission case. In addition, no eccentric shaft is needed by incorporating the planet gear assemblies in the speed reduction mechanism, and moreover, since no portion of the outside diameter line of the motor protrudes from the transmission case, the motor is allowed to occupy less space. Thus, the small and light transmission actuator can be provided in which no portion of the outside diameter line of the motor protrudes from the transmission case so that less space can be occupied, and which is made up of gears which can provide a good response in transmitting power and a high contact ratio for good efficiency.

Problems solved by technology

According to Patent Literature No. 1 above, however, since an outside diameter line of the motor protrudes from the transmission case, there is caused a problem that a limitation is imposed on the mounting position of the motor.

In addition, since the motor is exposed, there is also caused a problem that the motor may be damaged.

Furthermore, due to structural characteristics that the motor 71 and the drive gear 72 of the speed reduction mechanism are disposed concentrically and that the outside diameter line of the motor 71 protrudes largely outwardly of the drive shaft 71a, when the diameter of the motor is enlarged with a view to obtaining a large torque, since a center distance between a driven shaft 60a and the drive shaft 71a of the motor 71 is inevitably increased, the drive gear 72 and the driven gears 73, 74 have to be enlarged, which results in increases in mass and inertia moment, leading to a problem that the response in transmitting power is deteriorated.

On the other hand, when attempting to change gear ratios with the center distance being maintained, either the drive gear 72 or the driven gears 73, 74 should be made smaller in diameter, and since the stress the tooth face has to carry is increased while the diameter of the gear is decreased, from the viewpoint of maintaining the strength of the gear the tooth thickness needs to be increased, and, as has been described above, this triggers the problem that the mass is increased to thereby deteriorate the response.

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